Hermetically sealed connector

ABSTRACT

A hermetically sealed electrical connector capable of operation in temperatures from -55* to 225* C. As disclosed, it comprises an outer shell of light weight aluminum alloy, surrounding copper contacts extending through a glass insulator supported within the shell; the shell, the insulator, and the contacts being made from materials having specified coefficients of thermal expansion and yield strength effective to avoid destruction of the integrity of the seal by thermal expansion and contraction.

United States Patent [151 3,685,005

DAlessandro [451 Aug. 15, 1972 [54] HERMETICALLY SEALED 3,225,132 12/1965 Baas etal ..l74/50.6l X CONNECTOR 3,370,874 2/1968 Scherer et a1 ..174/5061 X [72] Inventor: W M. UAlessandm, Chicago, 3,371,413 3/1968 Rundle ..339/177 X OTHER PUBLICATIONS [73] Assignee: The nunker'Ramo Corporation Electrical Manufacturing, article by J. Comer Vol. 62

Oak Brook, No. 2 Aug. 1958 Pages 102- 107 [22] Filed: July 22, 1969 P Ex Ri h dE M nmary ammerc ar oore [21] Appl' 843,644 Attorney-Frederick M. Arbuckle [52] US. Cl. ..'.339/l36, 339/218, 339/278 ABSTRACT Int. Cl. A hemeticall a] d l y se e e ectrlcal connector capable of [58] new 3 32 operation in temperatures from -55 to 225 C. As & C disclosed, it comprises an outer shell of light weight aluminum alloy, surrounding copper contacts extending through a glass insulator supported within the [56] References C'ted shell; the shell, the insulator, and the contacts being D made from materials having specified coefiicients of UNITE STATES PATENTS thermal expansion and yield strength effective to 5 2 i;

avoid destruction of the integrity of the sea] by ther- 1 d t t 3,076,954 2/1963 Stanback ..339/278 x m expansm 3,109,054 10/1963 Kuhnapfel et a1. ..174/ 152 7 Claims, 2 Drawing figures PKTE'NTEDAHB 15 I972 INVENTOR FRANKLIN M. D'ALESSANDRO BY 2%ywnwzvfl ATTY.

HERMETICALLY SEALED CONNECTOR BACKGROUND OF THE INVENTION The invention relates generally to electrical connectors, and particularly to hermetically sealed connectors suitable for service in temperature environments ranging from very low to very high temperatures, yet light enough for use in aircraft and aerospace applications and capable for meeting certain military specifications for such use.

Hermetic electrical connectors generally employ two types of glass to metal seals, namely, a matched seal and a compression seal. With the matched seal, the metal and glass components exhibit similar coefficients of thermal expansion thereby preventing the development of excessive strains and undesirable stresses when the metal and glass contract and expand due to changes in temperature. This arrangement requires a chemical bond to be formed between the glass and metal to provide the seal.

The compression seal arrangement provides a seal between the glass and metal by a compressive force. It is desirable that a chemical bond also exist, but it is not necessary for this type of seal. The compressive force is exerted on an internal glass member by an outer metal shell having a relatively high coefficient of thermal expansion. After heating the glass and shell to a fusing temperature, the shell contracts during a cooling process to provide the compressive force on the glass member.

At this juncture it should be noted that glasses are very strong in compression and very weak in tension, and that a compression seal is possible only with an external metal member disposed about an internal glass member, whereas a matched seal can be accomplished with either an externally disposed metal member or an internally disposed metal member, i.e., a metal contact located in a surrounding glass body or member. Electrical connectors generally employ both types of seal arrangements since each connector necessarily has an external member, namely, a outer shell or housing structure and internally disposed metal members, namely, electrical contacts supported in an insulating glass body.

Hermetic electrical connectors presently available generally use, as the shell material, low carbon steels, stainless steels and other alloys having low coefficients of thennal expansion as compared to other metals. The

internal glass insulators or bodies generally have even lower coefficients of thermal expansion, the values being on the order of 9Xl0'/C. Since the glasses used have low expansion coefficients, the material of the connector contacts are similarly limited to low expansion, special purpose alloys necessary to provide a matched seal between the contacts and glass. The most common of these are the iron-nickel alloys though tungsten and molybdenum have been used as contact materials.

Connectors constructed with the materials described above offer adequate mechanical strength to withstand stresses developed under thermal shock conditions but are substantially heavier than the connectors of the present disclosure since the density of steel and iron alloys average as about 8g/cc as compared to 2.7g/cc for aluminum. Further, because of the high electrical resistance of low expansion alloys, heretofore generally used as contacts, prior art hermetic connectors have been characterized by high contact resistance and thus relatively low current carrying capabilities. For example, a low expansion alloy of iron and nickel (50 percent iron and 50 percent nickel), which is a commonly used alloy for making contacts, has an electrical conductivity value of 4 percent IACS (International Annealed Copper Standard) as compared to pure copper which has a conductivity value of 101 percent IACS.

Heretofore, attempts have been made at using aluminum shells in the construction of hermetically sealed connectors. In US. Pat. No. 3,371,413 issued to D.F. Rundle and assigned to the present assignee, there is shown an aluminum shell structure in combination with a steel ring bonded to the periphery of a glass body. The steel ring (with the glass) is then force-fitted into the aluminum shell to form a mechanical seal between the steel and aluminum. Such a structure gains the advantage of the light weight of aluminum but the mechanical seal between the metals of the ring and shell is not as reliable as a seal provided by fusion. Further, the force fitted seal is somewhat difficult to produce in large quantities because of extremely close tolerance requirements.

Another attempt at using aluminum as the material of a connector shell has simply involved the use of an aluminum shell in combination with the known low expansion glasses and low expansion alloy contacts. While gaining the advantage of the light weight of aluminum, the low expansion glasses in such aluminum connectors subject the seal interface and the aluminum shell to severe stresses because of the substantial difference in thermal expansion between the glass and aluminum. Aluminum alloys have a coefficient of thermal expansion on the order of 25 l0'/C. Further, most glasses have temperatures higher than the melting point of aluminum; most aluminum alloys melting at temperatures below 650 C., and in addition, the low expansion alloy contacts have the low electrical conductivity characteristic noted above.

Historically, the major difficulty in providing a hermetic connector in an aluminum shell has been the detrimental effect of the high coefiicient of thermal expansion value of aluminum. While a high compressive force can be exerted on the inner glass body by the aluminum, when the connector cools after the firing and sealing process, a correspondingly high tensile force is exerted on the shell. This tensile force produces stresses in the shell which can exceed the yield strength of the aluminum. When this occurs, the inner diameter of the shell wall deforms plastically and enlarges, thereby reducing the compressive force on the glass to a value proportional to the yield strength of the aluminum. Upon reheating, such as may occur during service, the seal expands elastically, and the stresses are reduced. Hence at sufficiently high temperatures, the

compressive force exerted by the shell on the glass is ble to withstand operating temperatures of over approximately l00 C.

It should be noted further that aluminum alloys are originally hardened by working and heat treating processes, and that most aluminum alloys suffer a decrease in their original hardness (i.e. their yield strength) when subjected to the firing process necessary for providing a connector with a hermetic seal. This firing process for providing the hermetic seal acts as an annealing process which tends to soften the aluminum of the shell. Thus, aluminum shells in the annealed condition are even less able to withstand the stresses exerted on the shell by the internal glass body.

BRIEF SUMMARY OF THE INVENTION The present invention provides a hermetically sealed electrical connector which is light in weight, has high electrical conductivity, and can withstand both low and high operating temperatures; i.e. temperatures in the range of from 55 C. (as required by some US. Military Specifications) to 225 C., without loss of the connectors hermeticity. This may be accomplished by using an outer shell structure made of a light weight aluminum alloy characterized by high yield strength (in an annealed or post-fired condition) and with a coefficient of thermal expansion greater than that of the glass (to provide compressive force thereon in cooling) but not so much greater than that of the glass as to permanently stretch or distort the metal of the shell and thus pre-dispose the connector to failure whenever subjected to such elevated temperatures in service.

THE DRAWING The invention, along with the objects and advantages thereof, will best be understood from consideration of the following detailed description taken in connection with the accompanying drawing in which:

FIG. I is a sectional view of a temperature-resistant hermetically sealed connector constructed in accordance with the principles of the invention; and

FIG. 2, is a sectional view of a preformed glass insulator used in construction of the connector of FIG. I.

PREFERRED EMBODIMENT Specifically, FIG. I shows a sectional view of a connector l constructed in accordance with the inventive principles presently to be disclosed. More particularly, the connector includes an outer shell or housing generally designated 12 but ordinarily including a mounting flange 14 and a receptacle portion 16 to receive a mating connector. In practice, this shell may include various forms of keyways 18, grooves 20 and coupling pins 22 as shown, but these form no part of the present invention.

The shell 12 does however have a central bore 24 extending through the mounting flange 14 and in communication with the receptacle portion 16 of the shell to provide for mounting the glass insulator 26 which in turn carries at least one metallic contact 28, each of which has a terminal portion 30 disposed exteriorly of the connector and an internal pin portion 32 within the receptacle 16. The glass insulator 26 is, of course, held in position and hermetically sealed within the bore 24; being fused to the internal walls of the bore 24 and to the individual contacts 28.

The outer shell 12 is made of a light weight aluminum alloy characterized by having a relatively high yield strength (for example 15,000 pounds per square inch or preferably 21,000 pounds per square inch or more in an annealed or post-fired condition) and having a coefficient of thermal expansion well above that of the insulator 26, but within certain limits: generally not exceeding 1 and A times the coefficient of the glass.

Excellent results are obtained by the use of glass having a CTE of l7Xl0' and an aluminum alloy having a CTE of about 23x10 /C. A metal having these qualities is 5083 Aluminum being a designation of the Aluminum Association, 420 Lexington Avenue, New York, N.Y., and of the USA Standards Institute. A complete designation system is found in the USAS Document H35. l-l967. The 5083 Aluminum is an aluminum alloy having a coefficient of thermal expansion of 23.4X10' /C. and an annealed yield strength of 21,000 per square inch at room temperature in the anneale d condition. The significance of this figure is seen when compared to the 8,000 psi value of annealed 6061 aluminum which is a popular commercial alloy.

The 5083 Aluminum is given as a metal suitable for the shell 12 of the present invention because of its desirable qualities; namely, its suitable yield strength, satisfactory coefficient of thermal expansion, and light weight. However, other metals having similar qualities may be employed for the purposes of the invention and even aluminum alloys have less then optimum qualities (such as 6056 which has a yield strength of 22,000 and CTE 26Xl0' /C. or 5086, which has a yield strength 16,000 and CTE 23.9Xl0' /C.) are considered satisfactory for some purposes.

The connector is provided with greatly increased current carrying capabilities (as compared with prior art hermetic connectors) by making the contacts 28 from a high electrical conductivity metal such as copper, which as mentioned earlier has a conductivity of 101 percent IACS as compared to the 4 percent value of the nickel-iron alloy. Further, copper has a coefficient of thermal expansion of l7 l0/C which is substantially higher than that of nickel-iron alloys.

To provide a matched seal between the contacts 8 and the insulator 26, and a compression seal between the insulator and the shell 12 at a temperature below the melting temperature of the shell, the insulator is made from a glass material having a relatively high coefficient of expansion (as compared with other glasses, but closely matched to that of the copper contacts) and a relatively low working temperature. A glass exhibiting these qualities is type Alf-l9 glass, manufactured commercially by Ferro Corporation, Cleveland, Ohio, though other glasses having the same or similar qualities may be used. The AL-l9 glass has an expansion coefficient of l7 l0/C., which is the same as copper, and is about two-thirds that of 5083 Aluminum, the expansion coefficient of 5083 Aluminum being 23.4Xl0"/C. Further, the working temperature of the ALI-l9 glass is approximately 540 C. which is below the melting temperature of 5083 Aluminum, the melting temperature of 5083 Aluminum being 555 C.

The glass insulator 26, is preferably a pre-formed, unitary member which is formed to have the correct size and shape to fit in the bore 24 of the shell 12 and to receive the contacts 28 before it is sealed in the shell. This may be accomplished by first grinding the glass material into a powder and then placing the powder in a mold (not shown) to be pressed and pre-fired to form a single piece pre-forrn as shown in FIG. 2. The preform is provided with chamfered or bevelled peripheral edges 34 and countersunk holes 36 for receiving the contacts 28. The chamfered edges and countersunk holes promote the development of a smooth, uniformly stressed glass fillet 38 between the contact members 28 and the outer shell 12 during a firing process for providing the seals. This is indicated by the uniform cross section and rounded corners of the insulating body 26 shown in FIG. 1. Without the pre-formed chamfer and countersunk holes, the glass tends to form irregular stress risers and depressions during the firing process.

After the glass insulator 26 is pre-formed, it is inserted and suitably located within the bore 24 through the shell 12. Hermetic seals are then provided between the metal of the contact and the glass, and between the metal of the shell and the glass by a firing process which heats the glass to its working temperature. At this temperature, the glass is softened to provide an adequate glow thereof within the shell and about the contacts, the glass forming a bond with the contacts.

With the cooling of the connector, the shell contracts on the glass insulator since the metal of the shell has a greater expansion coefficient (23.4Xl0' /C.) than that of the glass which is l7 10' /C. as explained above. The difference in the expansion coefficients of the glass and shell in the present invention, however, is not as large as those of prior art devices which use low expansion glasses (9Xl0' /C) in aluminum shells. Thus, in the present invention, the stress imposed on the shell 12 by the glass insulating body 14 is substantially lower than that of the prior art aluminum connectors. This lower stress characteristic, coupled with the high yield strength of the shell material, provides the connector of the present invention with highly reliable hermetic seals since the tendency of the shell to deform plastically is substantially reduced. In this manner, the thermal shock limit of the glass insulating body is substantially increased since the high yield strength of the shell maintains the glass in compression at operating temperatures substantially higher than heretofore possible with hermetic aluminum connectors.

Thermal shock tests were conducted on connector samples of the invention by rapidly changing the temperature of their operating environment from a low temperature value on the order of -55 C. to a high temperature value on the order of 225 C., and continuously operating the connectors at a minimum of 200 C. This was accomplished without the loss of hermeticity. The seals and glass thus withstood temperature extremes substantially greater than prior art aluminum which, as explained above, have a maximum operating temperature of about 100 C.

In addition to the extended temperatures at which the connector of the invention will operate in a reliable manner, the connector offers a substantial weight reduction over conventional steel and iron alloy connectors. This is of particular importance in the aerospace and aircraft industry where weight is a primary consideration.

Also, as heretofore explained, use of copper for the contacts provides the connector with greatly increased electrical conductivity over that of prior art connectors. In order to protect the copper of the contacts from excessive oxidation during the firing and sealing process, the contacts may be clad or plated with nickel, rhodium or other suitable oxidation resistant metals.

It should now be apparent from the foregoing description that the applicant has disclosed a highly reliable, hermetically sealed electrical connector which is light in weight, has high electrical conductivity and is thermally shock resistant over a range of temperatures never achieved by prior art devices.

Having thus described the invention, I claim:

1. A hermetically sealed electrical connector capable of maintaining hermetic integrity throughout a temperature range from as low as 55 C. up to at least 225 C. and comprising, in combination, a hollow metal shell of an aluminum alloy having an opening therethrough; the opening having side walls closely surrounding and engaging a glass insulator fused therein and in tight compression relationship therewith; with at least one electrical contact fused into said insulator and extending therethrough; said contact being of metal having a coefficient of thermal expansion matched to that of said insulator and being supported solely thereby; the glass having a working point lower than the melting point of the metal shell, and the metal shell having a coefficient of thermal expansion greater than that of the glass but not more than 1% times that of the glass and being characterized by a yield strength such that said glass insulator may be fused within the shell and thereafter cooled to 55 C. without imparting strains upon the metal shell which causes stresses exceeding the annealed yield strength thereof.

2. The device of claim 1 wherein the glass has a coefficient of thermal expansion of substantially 17 X l0"/ C. and the metal shell is an aluminum alloy.

3. The device of claim 1 wherein the metal shell is an aluminum alloy having a yield strength determined on said shell in an annealed condition of at least 15,000 pounds per square inch, and having a coefficient of thermal expansion of substantially 23.4 X l0"/ C.

4. The connector described in claim 1 in which the glass insulator is a unitary, pre-formed member having the peripheral edges thereof chamfered, and at least one countersunk hole for accommodating the contact, the chamfered edges and countersunk hold providing uniformly stressed fillets between the glass and the shell and between the contact and the glass.

5. A hermetically sealed electrical connector capable of maintaining hermetic integrity throughout a temperature range from as low as 55 C. up to at least 225 C. and comprising, in combination a hollow aluminum alloy shell having an opening therethrough; the opening having side walls closely surrounding and engaging'a glass insulator fused therein and in tight compression relationship therewith; with at least one copper electrical contact extending through the insulator and fused into said insulator and supported solely thereby; the glass having a working point lower than the melting point of the shell and substantially 540. C.

and having a coefficient of thennal expansion of substantially 17 X l"/ C. and the metal shell having a coefficient of thermal expansion of substantially 23.4 X

10 C. and being characterized by a yield strength w determined on the said aluminum shell in an annealed condition of at least 15,000 pounds per square inch so that said glass insulator may be fused within the shell and thereafter cooled to 55 C. without imparting strains upon the shell which cause stresses exceeding the said yield strength thereof.

6. The device of claim wherein the yield strength of the shell determined on the shell in an annealed condi- 

2. The device of claim 1 wherein the glass has a coefficient of thermal expansion of substantially 17 X 10 6/* C. and the metal shell is an aluminum alloy.
 3. The device of claim 1 wherein the metal shell is an aluminum alloy having a yield strength determined on said shell in an annealed condition of at least 15,000 pounds per square inch, and having a coefficient of thermal expansion of substantially 23.4 X 10 6/* C.
 4. The connector described in claim 1 in which the glass insulator is a unitary, pre-formed member having the peripheral edges thereof chamfered, and at least one countersunk hole for accommodating the contact, the chamfered edges and countersunk hold providing uniformly stressed fillets between the glass and the shell and between the contact and the glass.
 5. A hermetically sealed electrical connector capable of maintaining hermetic integrity throughout a temperature range from as low as -55* C. up to at least 225* C. and comprising, in combination a hollow aluminum alloy shell having an opening therethrough; the opening having side walls closely surrounding and engaging a glass insulator fused therein and in tight compression relationship therewith; with at least one copper electrical contact extending through the insulator and fused into said insulator and supported solely thereby; the glass having a working point lower than the melting point of the shell and substantially 540* C. and having a coefficient of thermal expansion of substantially 17 X 10 6/* C. and the metal shell having a coefficient of thermal expansion of substantially 23.4 X 10 6/* C. and being characterized by a yield strength determined on the said aluminum shell in an annealed condition of at least 15,000 pounds per square inch so that said glass insulator may be fused within the shell and thereafter cooled to -55* C. without imparting strains upon the shell which cause stresses exceeding the said yield strength thereof.
 6. The device of claim 5 wherein the yield strength of the shell determined on the shell in an annealed condition is at least 21, 000 pounds per square inch and the aluminum alloy is the aluminum alloy designated as 5083 Aluminum by the U.S.A Standards Institute.
 7. The connector described in claim 6 in which the glass insulator is a unitary, pre-formed member having the peripheral edges thereof chamfered and at least one countersunk hole for accommodating a contact; the chamfered edges and countersunk hole providing uniformly stressed fillets between the glass and the shell and between the contact and the glass when the connector is subjected to a firing temperature. 